1. Field of the Invention
The present invention relates to a method of growing a non-polar a-plane gallium nitride. More particularly, the present invention relates to a method of growing a non-polar a-plane gallium nitride single crystal using an MOCVD technique.
2. Description of the Related Art
In general, a gallium nitride single crystal is grown via a vapor phase growth method such as metal organic chemical vapor deposition (MOCVD) and hydride vapor phase epitaxy (HVPE), or a molecular beam epitaxy (MBE) method on a heterogeneous substrate such as sapphire (Al2O3) or silicon. In practice, the gallium nitride single crystal employed in the fabrication of a gallium nitride light-emitting device is grown along a c-axis direction [0001].
However, due to strong piezoelectric properties manifested in the c-axis direction, a piezoelectric field arises from stress at interfaces having different lattice constants. As shown in FIG. 1a, in a band diagram of an idealistic active layer free from stress, wave functions of electrons and holes are almost symmetrical. But as shown in FIGS. 1b and 1c, in case of influence of compressive stress or tensile stress resulting from different lattice constants, the piezoelectric field separates the wave functions of electrons and holes from each other as marked by a dotted line. This disadvantageously degrades recombination efficiency in an active layer of a gallium nitride device grown in the c-axis direction of the substrate. Further, an increased distance between the wave functions caused by such piezoelectric field tends to lengthen a light-emitting wavelength and potentially alter the light-emitting wavelength depending on the extent of voltage applied.
To solve these problems, U.S Patent Publication No. 2003/0198837 (published on Oct. 23, 2003, invented by Michael D. Craven et al.) teaches a method of growing a non-polar a-plane gallium nitride. It was confirmed that as a result of a test conducted based on the aforesaid method, the gallium nitride grew slowly. More specifically, as disclosed in the U.S. patent, the gallium nitride grew at a rate of merely 5 to 9 Å/s (1.8 to 3.24 μm/hr).
Moreover, as described in the U.S. Patent, it was confirmed that the non-polar a-plane gallium nitride could grow under a pressure of 0.2 atm or less. As is easily understood by those skilled in the art, this low-pressure condition for growth has a limit in obtaining a high-quality crystalinity. Also, before growing the non-polar a-plane gallium nitride, the pressure condition (typically 1 atm) for depositing a low-temperature nucleation layer should be changed to a low pressure condition for growing the gallium nitride. This disadvantageously complicates a process.